Narrative:

After the national weather service advised they were going to release the weather balloon in the next couple of minutes; I advised all aircraft in a blank transmission about this. Minutes later; I cleared a caravan for take off runway 10 when seconds later I observed the weather balloon midfield of runway 10 appearing to be in close proximity to the runway. Since it was hard to determine the position of the weather balloon; I advised the pilot of the situation and approved a deviation if the pilot needed. Seconds later I observed the caravan making a sharp turn to the left appearing to try to avoid the weather balloon and after the maneuver; resumed course without incident. Although for many years I never had an incident involving approving the release of the weather balloon; this was the first time I have became concerned with this procedure. The conditions placed the balloon almost over the runway. Changes in the procedures for approving balloon releases should be considered. I recommend that the balloon is released immediately as the approval is granted.

Related reports:

Google
 

Original NASA ASRS Text

Title: A SJU Controller observed a departure vs. a weather balloon conflict. He now questions the procedures for releasing the balloons.

Narrative: After the national weather service advised they were going to release the weather balloon in the next couple of minutes; I advised all aircraft in a blank transmission about this. Minutes later; I cleared a Caravan for take off Runway 10 when seconds later I observed the weather balloon midfield of Runway 10 appearing to be in close proximity to the runway. Since it was hard to determine the position of the weather balloon; I advised the pilot of the situation and approved a deviation if the pilot needed. Seconds later I observed the Caravan making a sharp turn to the left appearing to try to avoid the weather balloon and after the maneuver; resumed course without incident. Although for many years I never had an incident involving approving the release of the weather balloon; this was the first time I have became concerned with this procedure. The conditions placed the balloon almost over the runway. Changes in the procedures for approving balloon releases should be considered. I recommend that the balloon is released immediately as the approval is granted.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.